Lower Similkameen River 

Arsenic Total Maximum Daily Load 

Submittal Report 

For Joint Issuance 

January 2004 

Publication Number 03-10-074 

Lower Similkameen River 

Arsenic Total Maximum Daily Load 

Submittal Report 

For Joint Issuance 

Prepared by: 

Mark Peterschmidt 

Washington State Department of Ecology 

Water Quality Program

In Consultation With 

Lorraine Edmond 

United States 

Environmental Protection Agency 

January 2004 

Publication Number 03-10-074 
For additional copies of this document contact: 

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Table of Contents 

Page 

List of Tables................................................................................................................................. ii

List of Figures................................................................................................................................ ii

Executive Summary.....................................................................................................................iii

Introduction................................................................................................................................... 1

Components of the TMDL ........................................................................................................... 2

Background ................................................................................................................................... 3

Applicable Criteria ....................................................................................................................... 7

Water Quality and Resource Impairments ................................................................................ 9

Technical Approach and Results................................................................................................. 9

Loading Capacity........................................................................................................................ 10

Load and Wasteload Allocations............................................................................................... 10

Seasonal Variation ...................................................................................................................... 12

Margin of Safety.......................................................................................................................... 14

Summary Implementation Strategy.......................................................................................... 15

Activities that Support this TMDL ........................................................................................... 19

Monitoring Strategy.................................................................................................................... 19

Supporting Regulations and Land Management Plans........................................................... 19

Reasonable Assurance ................................................................................................................ 19

Public Participation .................................................................................................................... 20

References Cited.......................................................................................................................... 20

Definitions and Acronyms.......................................................................................................... 21

Appendix A................................................................................................................................ A-1

Appendix B ................................................................................................................................ B-1

Similkameen River TMDL Page i 
List of Tables 

Page 

Table 1.............................................................................................................................................4 

Table 2...........................................................................................................................................12 

Table 3...........................................................................................................................................13 

Table 4...........................................................................................................................................17 

List of Figures 

Figure 1 ...........................................................................................................................................5 

Figure 2 .........................................................................................................................................13 

Page ii Similkameen River TMDL
Executive Summary

Basin: Okanogan River (Washington) 

Sub-basin: Similkameen 

Key Impaired Resources: Water Quality 

Uses Affected: Class “A” water, Water Supply (Domestic), consumption of 

aquatic organisms 

Type of Impairment: Elevated concentrations of arsenic 

Pollutant: Arsenic 

Contribution Factors: Historic mining practices and Natural sources 

The Similkameen River originates in the Cascade Mountains along the international border 

between British Columbia and Washington State. The Pasayten River flows north out of 

Washington to join the Similkameen River in British Columbia. The Similkameen River then 

turns south to cross the border and meet the Okanogan River at Oroville, Washington. Mining, 

forestry, agriculture, and recreation are the major land-use activities. 

Under Section 303(d) of the federal Clean Water Act, the Similkameen River has been listed by 

Washington State for non-attainment of the EPA human health criteria for arsenic. A Total 

Maximum Daily Load evaluation was therefore conducted for the portion of the river that flows 

through Washington State, as required by the Clean Water Act. The major source of arsenic 

appears to be a legacy resulting from historical mining activities, mostly in British Columbia 

between Hedley and the U.S. border. The only significant sources identified in Washington were: 

1) Palmer Lake, likely arising from periodic flooding and sediment deposit by the Similkameen 

River and perhaps inputs from Sinlahekin Creek, and 2) re-suspension of contaminated 

sediments. It was determined that the Similkameen River naturally exceeds the EPA arsenic 

criteria upstream of the areas disturbed by mining near Hedley, BC. Under these circumstances, 

natural conditions constitute the water quality criteria. Because arsenic levels naturally exceed 

criteria, the loading capacity for the river is set equal to the natural background concentration of 

arsenic. 

Seasonal water quality targets are 0.4 – 0.6 μg/L total recoverable arsenic, and estimates are 

provided of the load reductions needed in British Columbia and Washington State to meet the 

targets. The targets make no allowance for the downstream increase in arsenic concentrations 

that might occur naturally as the Similkameen flows through British Columbia and Washington. 

If new data or analysis can provide a reliable estimate of what that increase would be, the 

numerical targets should be revised upward accordingly. 

Due to the natural and legacy nature of the contaminant sources, an arsenic monitoring plan is 

the suggested implementation action for the Similkameen River. The plan recommends: 1) 

periodic monitoring of arsenic in the Similkameen to further define the long term changes in the 

Similkameen River TMDL Page iii 
legacy load of arsenic, 2) renewing arsenic monitoring of the river in Washington if and when 

mining related cleanups are undertaken, and 3) monitoring the Similkameen River at Oroville 

during a significant high water event to characterize arsenic and sediment movement in the high 

water conditions. 

Page iv Similkameen River TMDL
Introduction 

Section 303(d) of the federal Clean Water Act mandates that the state establish Total Maximum 

Daily Loads (TMDLs) for surface waters that do not meet standards after application of 

technology-based pollution controls. The U.S. Environmental Protection Agency (EPA) has 

established regulations (40 CFR 130) and developed guidance (EPA, 1991) for setting TMDLs. 

Under the Clean Water Act, every state has its own water quality standards designed to protect, 

restore, and preserve water quality. Water quality standards consist of 1) designated uses, such as 

supporting cold water biota and providing a drinking water supply, and 2) criteria, usually 

numeric, to achieve those uses. When a lake, river or stream fails to meet water quality standards 

after application of required technology-based controls, the Clean Water Act requires the state to 

place the water body on a list of "impaired" water bodies and to prepare an analysis called a 

Total Maximum Daily Load (TMDL). 

The goal of a TMDL is to ensure the impaired water will attain water quality standards. A 

TMDL includes a written, quantitative assessment of water quality problems and of the sources 

that cause them. The TMDL determines the amount of a given pollutant that can be discharged to 

the water body and still meet standards; this is called the loading capacity. The TMDL also 

allocates that load among the various sources. 

The TMDL also must consider seasonal variations and include a margin of safety that takes into 

account any lack of knowledge about the cause of the water quality problem or its loading 

capacity. The sum of the individual allocations and the margin of safety must be equal to or less 

than the loading capacity. 

In addition to the mandatory components of a TMDL, the general purposes of this document are 

to: 

• Summarize data that document the stream segments exceeding state standards for arsenic. 

• Summarize the results of a technical assessment performed to identify probable sources 

of arsenic loading that cause increases in arsenic concentrations and an estimate of the 

magnitude of those impacts on stream arsenic concentrations [Johnson, 2002]. 

• Summarize actions recommended for meeting water quality standards. 

• Summarize monitoring that should be used to track TMDL implementation and 

determine progress toward attaining water quality standards. 

A Detailed Implementation Plan will be developed within a year of TMDL approval. Further 

public input will be sought to help prepare this plan, which will identify how, when, and where 

voluntary restoration activities will be implemented. Details of a monitoring plan will be 

developed. The Washington State Department of Ecology (Ecology) and other entities will 

provide technical assistance and seek additional funding for these activities. 

This Total Maximum Daily Load (TMDL) for arsenic in the Similkameen River basin addresses 

the two segments of the Similkameen River as included on the 1998 Section 303(d) list of 

Similkameen River TMDL Page 1 
impaired surface waters. The water body identification number for the Similkameen River 

addressed by this TMDL is: ND93YL. Additionally, the Similkameen tributary Palmer Creek, 

connecting Palmer Lake to the Similkameen River, was found to have significant loading of 

arsenic and is included in this TMDL. The Water Body ID for Palmer Creek is LE24CF. 

The Confederated Tribes of the Colville Reservation have asked EPA to issue this TMDL for 

those portions of the Similkameen River that are within Indian allotments and other Indian 

country, as that term is defined in 18 U.S. C. § 1151. Since the water quality standards issued for 

the Colville Indian Reservation by the U.S. EPA on July 6, 1989 do not apply to the Indian 

allotments and other Indian country lands outside of the Colville Reservation that are covered by 

this TMDL, EPA has used the Washington State water quality standards as guidance for 

developing those portions of this TMDL to be issued by the EPA. 

Components of the TMDL 

The five components of a TMDL, as required by the Clean Water Act and applied to this TMDL, 

are described below: 

Loading capacity 

The loading capacity is the amount of pollutant that a water body can receive without violating 

water quality standards. The loading capacity is allocated between waste load allocations, load 

allocations, natural background, and a margin of safety. In the Similkameen River basin, the 

water quality is naturally elevated in arsenic. The natural concentration of arsenic in the 

Similkameen River in British Columbia, upstream of mining activities, exceeds the applicable 

criteria, taking up the entire loading capacity of the river. 

Wasteload allocations 

A wasteload allocation is a portion of a receiving water's loading capacity that is allocated to a 

point source of pollution. The only permitted discharger of waste water to the Similkameen 

River is the city of Oroville Waste Water Treatment Plant (WWTP)under National Pollution 

Discharge Elimination System (NPDES) permit number WA-002239-0. Because there is no 

capacity for a measurable increase in arsenic in the river due to the WWTP discharge, an 

analysis of the potential impact of the discharge was conducted. This analysis used “worst case” 

inputs to evaluate the impact the discharge from the plant could have on the Similkameen water 

quality, and concluded that the impact would not be measurable. Based on this analysis, the 

Oroville WWTP wasteload allocation was calculated using the current capacity of the WWTP 

and the federal Safe Drinking Water Act standard for arsenic in municipal water systems. The 

derived wasteload allocation was found to be an insignificant impact to the water quality at a 

sensitive low-flow river condition. 

Load allocations 

The load allocation is that portion of the receiving water's loading capacity that is attributed to 

nonpoint sources of pollution or to natural background sources. The Similkameen River is over 

its loading capacity for arsenic compared to natural background at Princeton; therefore load 

allocations are zero for anthropogenic nonpoint sources. The load allocation for natural nonpoint 

Page 2 Similkameen River TMDL
sources is the load that would yield a concentration equal to the natural background 

concentration. Data needed to convert from this concentration to a load do not exist. 

Margin of safety 

EPA requires that a TMDL include a margin of safety to account for any lack of knowledge 

concerning the relationship between loads and water quality. In this TMDL, a major unknown is 

whether there would be a natural incremental increase in arsenic concentrations downstream of 

Princeton and, if so, what that rate of increase would be. The numeric targets and load reductions 

recommended to meet them assume no natural increase, thus constituting an implicit margin of

safety. 

The WLA for the Oroville WWTP has been set to the drinking water standard for the municipal 

water supply. The potential contribution of arsenic from the WWTP WLA has been examined 

and found to be insignificant at low flow river conditions when the Similkameen River would be 

most vulnerable to additional loading. 

Seasonal variation 

The Similkameen River’s natural background arsenic concentration fluctuates over each annual 

cycle. The arsenic concentration rises with the high water flows that typically occur in May and 

June. In the months from September through April, water flow volumes are substantially lower 

and the natural background concentration of arsenic is lower than in the spring, though the 

arsenic concentration still exceeds the water quality criteria. The goals for this TMDL have been 

set to reflect the seasonal change of the natural background concentration. Higher goals are set 

for the spring and early summer seasons to reflect the natural changes in background 

concentration. 

Background 

The 72-mile long Similkameen River originates in the Cascade Mountains along the international 

border between British Columbia and Washington State. It flows north out of Manning 

Provincial Park, then turns south to cross the border and meet the Okanogan River at Oroville, 

the last 27 miles being in Washington (Figure 1). The climate is semi-arid over much of the 

basin. Mining, forestry, agriculture, and recreation are the major land-use activities. 

The Similkameen drains 9,308 square miles, over 90 percent of which is in British Columbia. 

Peak flows normally occur in April to July as a result of snowmelt (Figure 2). Stream flow 

during the winter generally stays low due to freezing weather that maintains or contributes to the 

snowpack; exceptions occur when mild weather and heavy rain combine to cause flooding. The 

annual average discharge is 2,300 cfs; the average for September is 609 cfs (at Nighthawk, WA). 

Mining occurs at a number of locations in British Columbia, although a detailed accounting of 

the mining activity was not obtained for the present report. Pommen (2001) summarized the 

early gold mining as follows: “Placer gold mining took place in the 1860s and 1870s, and hard 

rock mining began in the late 1890s, with 1905-55 being the most productive period. There have 

been 77 past producers in the basin.” 

Similkameen River TMDL Page 3 
Shaw and Taylor (1994) mention the following mines in British Columbia: Similco Mines 

copper mine between the Similkameen River and Wolfe Creek, below Princeton; eleven placer 

mines along the Similkameen and Tulameen rivers, including the Dankoe silver/gold mine near 

the U.S. border; and the large Corona Nickel Plate Mine and Candorado Mines Ltd. near Hedley, 

which mine gold or process tailings for gold. As of 1994, other mines were proposed near 

Hedley. Similco is currently in caretaking status. The Nickel Plate and Candorado mines have 

been closed and under reclamation since about 1997. 

Downstream of the border, the Similkameen flows though arid sagebrush terrain typical of northcentral Washington. Approximately six miles below the border, the river meets Palmer Lake 

outlet, sometimes called Palmer Creek. A unique hydrologic feature of their juncture is that, 

during the spring, high flows in the Similkameen can cause Palmer Creek to reverse direction 

and the river flows into the lake. Based on observations during the technical study (Johnson 

2002), this appears to occur at flows greater than 5,000 cfs. Other than Palmer Lake, Washington 

tributaries to the Similkameen are dry most of the year, except at higher elevations. 

Table 1: Water Body Identification Numbers for water bodies addressed in this Similkameen 

River Arsenic TMDL

Water Body Name New Water Body

ID Number 

Old Water Body

ID Number 

Included in 

1996 303(d) 

List for arsenic 

Included in 

1998 303(d) 

List for arsenic

Similkameen River ND93YL WA-49-1030 No Yes 

Palmer Creek LE24CF -NA- No No 

Page 4 Similkameen River TMDL
Similkameen River TMDL Page 5 
Page 6 Similkameen River TMDL
Applicable Criteria 

Within the state of Washington, water quality standards are published pursuant to Chapter 90.48 

of the Revised Code of Washington (RCW). Authority to adopt such rules, regulations, and 

standards as are necessary to protect the environment is vested with the Department of Ecology. 

Under the federal Clean Water Act, the EPA Regional Administrator must approve the water 

quality standards adopted by the state (Section 303(c)(3)). Through adoption of these water 

quality standards, Washington has designated certain characteristic uses to be protected and the 

criteria necessary to protect these uses [Washington Administrative Code (WAC), Chapter 173-

201A]. 

Streams in the Similkameen watershed are designated as Class A as designated under WAC 173-

201A-120(6). The characteristic uses designated for Class A waters and protection in 

Similkameen River basin streams are as follows (Chapter 173-201A WAC): 

"Characteristic uses. Characteristic uses shall include, but not be limited to, the following: 

(i) Water supply (domestic, industrial, agricultural). 

(ii) Stock watering. 

(iii) Fish and shellfish: 

- Salmonid migration, rearing, spawning, and harvesting. 

- Other fish migration, rearing, spawning, and harvesting. 

- Clam and mussel rearing, spawning, and harvesting. 

- Crustaceans and other shellfish rearing, spawning, and harvesting. 

(iv) Wildlife habitat. 

(v) Recreation (primary contact recreation, sport fishing, boating, and aesthetic 

enjoyment). 

(vi) Commerce and navigation." 

This TMDL is designed to address impairments of characteristic uses caused by elevated arsenic 

concentrations. 

WAC 173-201A contains arsenic criteria to protect aquatic life. Because this criteria does not 

protect all designated uses for class A waters (i.e. use of water as a domestic supply and 

harvesting of organisms), the Clean Water Act requires the use of the water quality criteria set in 

National Toxics Rule, Chapter 40 of the Code of Federal Regulation part 141.36 (40CFR131.36). 

The National Toxics Rule defines the criteria for arsenic for the protection of human health. The 

numeric arsenic criterion is 0.018 μg/l for the consumption of water and organisms. In this case, 

the natural background value of the Similkameen River exceeds the NTR criterion at Princeton, 

BC, which is high in the watershed and upstream of the areas disturbed by gold mining activity. 

Similkameen River TMDL Page 7 
WAC 173-201A-070 is applicable to the Similkameen River’s condition where the natural 

background arsenic concentration is higher than the arsenic criterion in the NTR. Sub-part 2 

states: “Whenever the natural conditions of said waters are of a lower quality than the criteria 

assigned, the natural conditions shall constitute the water quality criteria.”

The Safe Drinking Water Act was applied in determining the reasonable maximum loading from

the city of Oroville municipal WWTP. Discharge of arsenic from the WWTP is controlled by the 

concentration of arsenic in the drinking water. The city of Oroville has a municipal water source 

that complies with the maximum contaminant level for arsenic in drinking water set in 

40CFR141.62. 

Page 8 Similkameen River TMDL
Water Quality and Resource Impairments

The Similkameen River was included in Washington’s 1998 list of impaired waters compiled 

under section 303(d) of the Clean Water Act. The 1998 listings for the Similkameen river 

included two segments for arsenic (segment locations by township-range-section: 40N 25E 13 

and 40N 27E 28) and one segment for temperature (40N 27E 28). This TMDL addresses only the 

arsenic listings. The Similkameen River consistently has higher concentrations of arsenic than 

other water bodies in Washington. The Similkameen River was included on the 1998 303(d) 

based on data collected at the Nighthawk Bridge in 1995 and 1996. 

Technical Approach and Results 

An approach of mass balancing was used in TMDL evaluation for arsenic in the Similkameen 

River. The mass balancing was used to evaluate the sources of arsenic loading and their potential 

impacts to the Similkameen River water quality. This study approach used several techniques for 

the collection of surface water data, sediment data, and discharge information from the Oroville 

WWTP, the only permitted discharger in Washington. Data collected was used to provide 

assessment of potential arsenic sources and to provide for the comparison data from the current 

study to other data sources. (Johnson 2002) 

Routine monitoring for arsenic in the Similkameen was provided for the TMDL by including 

arsenic in the monthly monitoring program maintained by Ecology’s Environmental Assessment 

Program’s Freshwater Monitoring Unit. The monthly monitoring was conducted at stations 

49B070, Similkameen River at Oroville and 49B110, Similkameen River at 

Chopaka Bridge, B. C. 

Intensive sampling surveys were conducted for the Similkameen River mainstem and for 

tributary streams that enter the river in Washington State. Tributary stream and mainstem

sampling occurred together during the intensive sampling events. Coupling these sampling 

studies allowed for the direct comparison of the stream inputs and the loads measured in the river 

itself. The intensive sampling did reveal that Palmer Creek, the outlet from Palmer Lake, is a 

significant arsenic source to the reach of river within Washington. 

Sediment data used in the technical assessment were collected by Ecology staff and staff of the 

Colville Confederated Tribes (Hurst, 2003). The sediment data revealed values of arsenic as high 

as 230 mg/Kg. These reported sediment values are sufficient to create water quality impairment 

if they were to be re-suspended into the water column. 

The concentration of arsenic in Palmer Creek appears to be associated with the sediments that 

accumulate in the reach of the Similkameen between river mile 19 and river mile 24. Stream

channel morphology and grain size distribution in the Similkameen /Palmer Creek complex are 

indicative of deposition of sediments in this reach. The high flows in the Similkameen associated 

with spring run off carry large sediment loads into this reach; this includes Palmer Creek when 

high flows from the Similkameen River inundate the creek and backs into Palmer Lake. The 

Similkameen River TMDL Page 9 
elevated arsenic values in the sediments and waters of this reach are likely a result of the 

sediment deposition from sources higher in the watershed. 

Loading Capacity 

Loading capacity is the ability of a water body to receive pollutants and remain within applicable 

water quality criteria. The Similkameen River upstream of mining disturbances naturally exceeds 

the water quality criteria set in the NTR. Due to the natural concentrations of arsenic in the river, 

the loading capacity for the Similkameen River is taken up by the natural background loading to 

the river. The result of the natural loading is that there is no available loading capacity to allocate 

to other significant point or anthropogenic non-point sources of arsenic. The natural background 

arsenic concentration is used as the loading capacity and as the TMDL target concentration for 

this TMDL. 

Derivation of the natural background concentration is described in detail in the attached TMDL 

Evaluation Report, (TMDL Appendix B), pp 35-39. The analysis uses data from Princeton, BC, a 

monitoring station upstream from the areas impacted by mining. Data from 1990-1999 were 

summarized and the results were compared to similar data from some of the least disturbed 

watersheds in Washington’s ambient monitoring database. The natural background arsenic 

concentration, and the corresponding loading capacity, varies seasonally from 0.4 to 0.6 ug/l (see 

Table 3 below). 

Load and Wasteload Allocations 

The “load allocations” and “wasteload allocations” are the portions of the stream's loading 

capacity that are designated, or “allocated,” for each source of pollution. “Wasteload Allocation” 

refers to that portion of pollution that originates from point sources or permitted discharges to the 

water body. “Load Allocation” refers to the non-point sources of pollution. 

No localized, non-point sources of arsenic were detected in Washington as a result of the present 

investigations. No load allocations were made for anthropogenic non-point sources. The natural 

load takes up all of the assimilative capacity of the river resulting in the allocation for natural 

sources being set equal to the natural background concentration. 

The data that would be required to convert from the natural background concentration to a 

natural nonpoint source load throughout the basin do not exist. The TMDL Evaluation report 

(Appendix B, p 42) does include estimated load reductions required to meet water quality targets 

at three locations. 

The single wasteload allocation assigned in this TMDL is for the city of Oroville’s Waste Water 

Treatment Plant (WWTP). The city of Oroville WWTP is the only permitted discharger to the 

Similkameen River. The city of Oroville discharges under the authority of their National 

Pollution Discharge Elimination System (NPDES) permit number WA-002239-0. 

Page 10 Similkameen River TMDL
The Oroville waste water treatment plant discharges waste water with a concentration of arsenic 

that does not appear significantly different than the arsenic concentration in the municipal water 

system for the city of Oroville. These concentrations are approximately 3 μg/L. Municipal water 

collected by the waste water system does not appear to change in arsenic concentration as it 

moves from the ground water source to the WWTP. 

Because there is no load capacity for a measurable increase in arsenic in the river due to the 

WWTP discharge, an analysis of the potential impact of the discharge was conducted. In order to 

ensure protection of water quality, this analysis used “worst case” scenario inputs to evaluate 

how much the discharge from the plant might increase the arsenic concentration in the 

Similkameen River. The inputs included the lowest reasonable flow in the river combined with 

the highest flow from the current plant along with the highest arsenic concentration that the 

city’s drinking water system could provide to the WWTP. 

The revised standard for arsenic in drinking water under the federal Safe Drinking Water Act is 

10 μg/L. The worst case contribution from the Oroville WWTP was determined using the 

allowable concentration of arsenic in the municipal water system combined with the 0.49 million 

gallons per day design capacity of the wastewater treatment plant. This resulting worst case 

arsenic load would be 19 g/day. 

At a loading rate of 19 g/day, Oroville WWTP would have an essentially undetectable effect on 

arsenic concentration in the Similkameen River. This conclusion was derived by considering the 

potential effect of the loading from the treatment plant on a “7Q10” river low flow condition. A 

7Q10 low flow is the lowest flow averaged over a seven day period that would be expected to 

occur once every ten years. The Similkameen River’s 7Q10 low flow of 186 cfs is most likely to 

occur during the August to March portion of the annual cycle which has the most restrictive 

target arsenic concentration of 0.40 μg/L (Johnson 2002). In a case where the river meets the 

0.40 μg/L target value and experiences a 7Q10 low flow, an arsenic concentration of 10 μg/L in 

the effluent from the Oroville WWTP operating at the design capacity calculates to a 

downstream concentration of 0.44 μg/L after mixing. This would be essentially an undetectable 

effect on arsenic concentration in the Similkameen River. 

The WLA for the Oroville plant is set to 19 g/day, with a concentration not to exceed 10 ug/l 

because the worst case evaluation showed this potential loading to have an undetectable effect on 

the river. 

There are several reasons to base the wasteload allocation for the arsenic discharge from the 

Oroville WWTP on the arsenic standard in the federal Safe Drinking Water Act. These reasons 

include, but are not limited to: acknowledging the small data set available on the discharge from

the waste water treatment plant, recognizing a single regulatory value for the municipal water 

system, and providing a stable target for the municipal system that does not fluctuate seasonally. 

Current data on the WWTP discharge concentration of arsenic consists of only two data points. 

These data points may not be truly representative of the WWTP discharge. Setting a WLA based 

on the small data set could be unfairly restrictive to the city when expansion of the system is 

needed or if other changes are needed to the municipal water/waste water system. Because the 

source of the municipal system is ground water, any expansion that required new wells could

Similkameen River TMDL Page 11 
result in a slightly different arsenic content. Future upgrades to Oroville’s municipal

water/wastewater systems should examine water quality data from the municipal source water 

and discharge data to assure all known and reasonable treatments are incorporated into the 

water/wastewater systems improvements to protect the water quality of the municipal drinking 

water and the Similkameen River. 

Using the federal Safe Drinking Water Act standard as a basis for the WLA makes the regulation 

of the municipal water system consistent. Changes to the system, such as replacing a municipal 

supply well, will need to address drinking water standards and the TMDL WLA through 

compliance with a single standard. A cautionary note on this is that the city will need to watch 

for industrial practices that have the ability to concentrate minerals in water, potentially raising 

the concentration of arsenic in water above that supplied in the city’s potable water. 

Seasonal variability of arsenic in the municipal water system cannot be determined with the 

currently available data. Using the Safe Drinking Water Act as a basis for the WLA provides 

assurance that the WLA can be attained throughout the year. There will not be significant 

seasonal impacts from a WLA that does not vary seasonally. The WLA is considered to have 

insignificant impact at river low flow conditions with the most restrictive target value and its 

impact on the river will be even less at higher flows. 

Table 2: Waste Load Allocation 

Waste Load Allocation 

Discharger NPDES Permit Number Pollutant Daily Load Allocation 

Oroville WWTP WA-002239-0 Arsenic 19 grams / day 

≤ 10 ug/l 

Seasonal Variation 

Analytical data on the arsenic concentrations in the Similkameen River was examined from

sources that included sample collection points in Washington and British Columbia. The arsenic 

concentration data used in this TMDL has been specifically targeted to river discharge volumes, 

but by comparing data collection dates to river flow data, an estimate of seasonal variation can 

be developed. The data review indicated that fluctuation of the arsenic concentration in the river 

occurs seasonally at Oroville, WA, at Chopaka, BC, near the international boundary and above 

the Princeton where natural background values for the TMDL are established. The seasonal 

variation appears to be tied to the seasonal fluctuation of the river flow, with the highest 

measured values having been measured at river stages that are rising and nearing the spring peak 

flows. 

The Total Maximum Daily Load Evaluation for arsenic in the Similkameen River (Appendix B) 

included monthly monitoring of arsenic at the Chopaka and Oroville bridges over the 

Similkameen. Data from 2000 - 2001 followed the pattern of higher concentrations in the spring 

flows tapering off to a more modest level as the river flow volumes diminished and stabilized 

over the remainder of the year (figure 2). This data from monthly monitoring from May 2000 to 

June 2001 occurred over a period when the Okanogan valley received a record low amount of 

Page 12 Similkameen River TMDL
precipitation, resulting in river lows approximately half of normal with only modest spring peaks 

of flow and arsenic. 

Figure 2: Total Recoverable Arsenic Concentrations Measured in Monthly Monitoring of Similkameen 

River from May 2000 to June 2001 (Ecology data) 

The seasonal variation in the background data taken from the Similkameen River at Princeton is 

used to determine the seasonal targets for the TMDL. The Princeton monthly average 

concentrations are presented in Table 3. These averages vary little over the year, yet represent 

substantial differences in loading due to the higher river flows associated with the higher spring 

values. 

Table 3: Proposed Targets for Total Recoverable Arsenic in the Similkameen River 

Month Target Concentration (μg/L)

May-June 0.6

April & July 0.5 

August - March 0.4 

Similkameen River TMDL Page 13 
Margin of Safety 

The federal Clean Water Act requires that a margin of safety be identified to account for 

uncertainty when establishing a TMDL. The margin of safety can be explicit in the form of an 

allocation, or implicit in the use of conservative assumptions in the analysis. Several 

conservative assumptions and critical conditions used in the development of the Similkameen 

River TMDL provide an inherent margin of safety as required by the statute. 

In this TMDL, a major unknown is whether there would be a natural incremental increase in 

arsenic concentrations downstream of Princeton and, if so, what that rate of increase would be. 

The numeric targets and load reductions recommended to meet them conservatively assumes no 

natural increase, thus constituting an implicit margin of safety. 

The WLA for the Oroville WWTP has been set using a conservative approach of examining 

“worst case” conditions for the WWTP discharge. Setting the WLA by using the 10 μg/L arsenic 

standard in the federal Safe Drinking Water Act, (a value about three times higher than the 

available data suggests) provided additional margin of safety to the TMDL. This standard was 

selected due to the WWTP discharge of arsenic is controlled by the municipal water entering the 

WWTP. The potential contribution of arsenic from the WWTP WLA, at maximum capacity of 

the plant and the maximum concentration allowed by drinking water standard, has been 

examined and found to be insignificant at river low flow conditions that would make it 

susceptible to additional loading. 

There is substantial uncertainty in the quantification of tributary loads within Washington. Only 

four samples were obtained from the major source identified, Palmer Creek, and its average flow 

to the river was estimated. It seems unlikely, however, that the load is seriously under or 

overestimated given the consistent difference observed between the arsenic concentrations at 

Chopaka Bridge and Oroville. 

Other than Palmer Lake outlet, Washington tributaries to the Similkameen are dry most of the 

year. No data were collected to establish tributary loading during storm or snow melt events. 

There is nothing in the available data to suggest that there are large unaccounted for arsenic 

inputs to the river within Washington during runoff events. 

Page 14 Similkameen River TMDL
Summary Implementation Strategy 

Implementation Overview

Under section 303(d) of the federal Clean Water Act, the U.S. Environmental Protection Agency 

requires states to identify impaired water bodies. The Similkameen River was included on 

Washington State’s 1996 and 1998 303(d) lists for arsenic. In 1999, Ecology identified the 

Similkameen River as a candidate to conduct a TMDL. Ecology used existing data and 

conducted field work between May 2000 and February 2002 to document conditions. After 

review from the Okanogan Watershed Implementation Committee and the Colville Confederated 

Tribes, Ecology published the TMDL technical report: A Total Maximum Daily Load

Evaluation for Arsenic in the Similkameen River (Appendix B). The technical report identified 

historic mining practices in the upper watershed as the primary source of elevated arsenic values 

in the Similkameen River. The technical report also recognized the existence of natural and 

anthropogenic factors that contribute to elevated arsenic values in the water. The Summary 

Implementation Strategy (SIS) summarizes a strategy to monitor the water quality to improve 

our understanding of this watershed, explore the legacy of arsenic contamination, and provide 

adaptive management strategies for long term improvement of water quality in the watershed. 

An SIS is needed to meet the requirements of a TMDL submittal for approval as outlined in the 

1997 Memorandum of Agreement between EPA and Ecology. It presents a clear, concise, and 

sequential concept of how the Similkameen River and its primary tributary, Palmer Creek, will 

ultimately meet the water quality standards over time. This SIS complies with the federal 

mandate of the Clean Water Act, Washington State laws to control point and non-point source 

pollution, and the 1997 Memorandum of Agreement between EPA and Ecology. 

This SIS will serve as guidance for developing a Detailed Implementation Plan (DIP) during the 

one year period after the TMDL has been approved. The DIP will describe specific 

implementation activities that need to be performed to achieve the TMDL targets. The DIP will 

also present a thorough plan for monitoring implementation of this TMDL. It is anticipated that 

implementation of this TMDL will document long term reductions in the arsenic carried by the 

Similkameen River waters. 

This is a plan to monitor and protect water quality. It is based in large measure on existing 

United States Federal and Washington State laws and regulations, county ordinances, and the 

voluntary actions of Canadian based entities. Implementation of this TMDL relies on the 

continued improvement of modern mining practices and continued vigilance of the water quality. 

The only NPDES permitted point source, the Oroville Wastewater Treatment Plant, contributes a 

negligible amount of arsenic to the loading in the river and does not result in a measurable 

increase of arsenic in the river. 

The restoration timeframe for this TMDL is very uncertain. A downward (improving water 

quality) trend in arsenic concentrations has been noted in data collected from the Chopaka 

Bridge water quality sampling station 49B110 (Similkameen R. @ Chopaka Br., B. C.). The 

downward slope in this data from 1984 to 2000 is different from spring to fall, and the inability 

to determine the source of this improvement weakens any estimates of the restoration timeframe. 

Similkameen River TMDL Page 15 
Examining the trend in the September data from the period of 1984 to 1999, the trend suggests 

that the Similkameen River at Chopaka would achieve the target around the year 2015. 

Exclusion of the earlier data and considering the trend in the data from 1990 to present makes the 

improving trend less evident. Many factors, such as natural shifting of the river channel or severe 

flooding, can potentially alter or reverse the improvement by re-suspending sediments that have 

been deposited in the river course or floodplain. Additionally, the Similkameen River has been 

shown to receive significant arsenic loading below the Chopaka Bridge station, probably 

associated with sediment deposits from up-river sources. Additional time and data are needed to 

address this loading. At this time, an optimistic view would be to see the TMDL goal reached at 

the Chopaka Bridge station within two decades, and at the Oroville water quality sampling 

station three decades after that. A more realistic view of the situation is to recognize that there 

have been more than a hundred years of mining history in the drainage and that the mining 

related enrichment of arsenic in the water and sediments will take many more years to be 

mitigated. 

Implementation Activities 

This TMDL is addressing water quality impairment from legacy loading and natural conditions. 

The technical report identifies monitoring activities for the implementation of the TMDL. A 

downward trend of arsenic concentrations in the Similkameen was identified in the technical 

report. The downward trend in arsenic concentrations may be due, in part or in whole, to changes 

in analytical techniques over the time monitoring has occurred. Additional monitoring will 

indicate if this downward trend continues and identify long term changes to this river system. 

Implementation Activities to Monitor Non-Point Sources: 

The TMDL technical study revealed that a reach of the Similkameen River that receives a 

substantial portion of the arsenic loading is a short reach of river characterized by features 

indicative of sediment deposition. This reach includes braided river beds and a unique interaction 

with Palmer Lake and the connecting stream, Palmer creek. This unique interaction is 

characterized by reversal of the flow of water in Palmer creek and significant rises in the 

Similkameen River flow. The reversal of flow reaches into Palmer Lake allowing sediments 

from the Similkameen River to be deposited in the lake and floodplain surrounding Palmer creek 

and the Similkameen River. The deposits of sediment in this area during high flows in the 

Similkameen appear to be a source of the arsenic in the river through the remainder of the year. 

Non-point sources of arsenic were not characterized sufficiently to separate natural sources from

anthropogenic influenced sources. Monitoring for changes in the non-point loading will likely be

done at the bridge crossing at Oroville. Additional monitoring is needed in order to determine 

whether re-suspension of bank sediments in Palmer Lake and Palmer Creek is increasing instream arsenic concentrations. 

Point Sources 

The Similkameen River TMDL technical report identified the Oroville Wastewater Treatment 

Plant (WWTP) as the only NPDES permitted point source in the watershed. Analysis of the 

effluent from the Oroville WWTP revealed a concentration of arsenic of 2.85 micrograms per 

liter. The source of the arsenic in the WWTP discharge appears to be the domestic water supply 

in Oroville. 

Page 16 Similkameen River TMDL
The Oroville water supply complies with the federal Safe Drinking Water Act with an arsenic 

concentration of approximately 3 micrograms per liter, well below the 10 micrograms per liter 

allowed by the federal Safe Drinking Water Act. This appears to be unchanged in concentration 

as the water passes through the system and into the WWTP. Monitoring the arsenic discharge of 

the Oroville WWTP will be incorporated into the NPDES permit during the permit cycle that 

follows the issuance of this TMDL. 

Table 4: This table presents general actions and entities responsible for implementing such actions. The 

information listed in the table is part of the overall strategy and may change as personnel and 

monetary resources are better defined during the development of the DIP. 

Entity Responsibilities to be met 1 2 3 4 5 6 7 8 9 10 Beyond 

10 Years

Ecology Periodic Monitoring of the 

Similkameen River, Monthly 

monitoring for a year repeated on 

every 5th year 

X X X

Ecology, 

local 

Monitor during high water events that 

would be expected to reoccur on a 10 

year interval (flow of 27,030 CFS or 

greater). 

X X X X X X X X X X X

City of 

Oroville 

Monitoring arsenic in wastewater

treatment plant discharge in

accordance with NPDES permit 

requirements 

X X X X X X X X X X X

Ecology/ 

Local 

Dredge Sampling Project. Field data 

collection for effect of recreational 

dredges on arsenic load in the 

Similkameen 

X

Responsible Entities and Actions 

Monitoring: The Department of Ecology is the entity currently conducting monthly water quality 

monitoring at the ambient water quality station on the Similkameen River (49A190 Okanogan 

River @ Oroville). Periodic monitoring would be preformed as part of this water quality 

monitoring function. 

Ecology is seeking a local partner to perform high water (flood) events. Ecology would retain the 

responsibility for analysis of the samples, but a local entity (i.e.: Conservation District, Irrigation 

District or city) would be much better situated to provide the labor to sample river flows on a 

short notice. 

Ecology is planning to conduct a field investigation of the potential impacts of recreational 

dredging on the arsenic loading in the water column. Ecology will be seeking a local dredge 

operator to voluntarily participate in this proposed study. Ecology will be investigating the 

protectiveness of the applicable regulations for recreational dredges. 

Similkameen River TMDL Page 17 
Ecology is the responsible entity for determining compliance of interim and final targets. 

Adaptive Management 

These implementation activities are centered on the gathering of long term data for the 

evaluation of water quality. These monitoring activities will serve to better define the rate that 

the water quality in the basin is improving. Re-evaluation of the long-term trends with the 

additional data will allow the restoration timeframe to be determined with greater precision. If 

the water quality monitoring activities show unexpected long term rises in arsenic values in the 

Similkameen River, an examination of any potential new sources of arsenic should also be 

undertaken. Additionally, intensive surveys and watershed investigation should be sought to 

identify significant events in the watershed that could re-suspend sediments. 

Persistent elevated values of arsenic or data that does not show the expected gradual decline of 

arsenic over time will trigger additional investigation under adaptive management. This should 

include the investigation of arsenic cycling in Palmer Lake as it relates to the flood-deposited 

sediments from the Similkameen River. The investigation of these flood deposits should also 

consider the interaction on ground water with the surface waters in the same reach of the river 

that received the greatest amount of sediment deposits. Further action may also include the 

coordination with upstream B.C. land management agencies to discuss upstream measures that 

would decrease flooding in the Palmer Lake /Similkameen River basin. 

Potential Funding Sources 

Funding sources will be more fully explored in the development of the DIP. At this time, funding 

for the periodic (repeating every five years) monitoring of the Similkameen River at the Oroville 

Station is expected be accomplished with little funding, provided that arsenic sampling can be 

incorporated into the routine monthly water monitoring that takes place at that location.

Incorporating the arsenic monitoring into the routine monitoring will require little additional time 

and labor of the sampler and no additional mobilization cost. Analysis for arsenic in the river 

water is a relatively inexpensive analysis. 

Sampling of a high water event would ideally be conducted through a local entity. This would 

facilitate sampling a high water event at short notice. Grant funding will be sought to fund this 

portion of the monitoring plan. 

Detailed Implementation Plan 

A Detailed Implementation Plan will be prepared within a year following approval of this 

document. Further public input will be sought to help prepare this plan. The plan will identify 

how, when, and where monitoring activities will be implemented. Ecology and other entities will 

provide technical assistance and seek additional funding for these monitoring activities and any 

restoration activities that may be identified as the body of data grows. It is the goal of this TMDL 

to meet the water quality arsenic standards by 2020. 

Page 18 Similkameen River TMDL
Activities that Support this TMDL 

Monitoring Strategy 

The implementation strategy for the Similkameen arsenic TMDL is designed to address a legacy 

loading of arsenic in the watershed by historic mining practices and the permitted discharge in 

the watershed. Implementation activities include 1) monitoring of the river mainstem

periodically at the Oroville station, 2) monitoring potential impact of high river flows through 

focused monitoring when a ten-year high flow (flow of 27,030 CFS or greater) occurs, 3) 

monitoring the discharge of the NPDES permitted WWTP at Oroville is a requirement of the 

permit itself.

Supporting Regulations and Land Management 

Plans 

Routine implementation of Washington’s State Environmental Policy Act, the Okanogan County 

Comprehensive Plan and the Okanogan County Shoreline Master Program will assure the review

of projects proposed in the vicinity of the Similkameen River for potential environmental 

impacts. This review process should ensure best management practices are used for new projects 

and that permitted activities will not impact the implementation of this TMDL. 

Reasonable Assurance 

During the development of the Similkameen River arsenic TMDL, available data for water 

quality throughout the watershed was collected and evaluated. The mass balance approach to the 

TMDL and the quantity of data has left questions regarding the amount of the natural arsenic 

contribution is in the watershed. The conservative assumptions used in the technical evaluation 

(Johnson 2002) burdens the anthropogenic sources with the potential natural loading below 

Princeton. Additional data on natural contribution could only raise the TMDL target higher than 

they have currently been set. 

The single NPDES permitted source to discharge to the river, the Oroville WWTP, has been 

found to be an insignificant contributor to the arsenic loading. The conditions used to determine 

the potential impact of the WWTP have been incorporated in the current NPDES permit. 

Monitoring the discharge water will be a condition of the NPDES permit and monitoring the 

source of the municipal water is currently being accomplished under the drinking water system

regulations administered by the Washington State Department of Health. 

Each of these conservative measures will assure that the Similkameen Watershed will be 

monitored and protected from activities that would threaten the water quality while the legacy 

loading is mitigated through time and nature. 

Similkameen River TMDL Page 19 
Public Participation 

Public involvement is a required part of the TMDL process. The public participation activities 

performed to date for this TMDL are included in appendix A “Summary of Public Involvement”. 

Additional public involvement activities will be included in preparation of the Detailed 

Implementation Plan. 

References Cited 

Hurst, Donald. 2003. Analysis of Sediment from the Similkameen River and Palmer Creek, US. 

Unpublished report for the Colville Confederated Tribe, Department of Environmental Trust. 

Johnson, Art, November 2002. A Total Maximum Daily Load Evaluation for Arsenic in the 

Similkameen River, Washington State Department of Ecology, Olympia, Washington. 

http://www.ecy.wa.gov/biblio/0203044.html (This report has been included as Appendix B to 

this report) 

Pommen, L. 2001. E-mail to Art Johnson, December 4. B.C. Ministry of Water, Land and Air 

Protection. 

Shaw, R. and B.R. Taylor. 1994. Assessment of Federal –Provincial Water Quality Data for the 

Flathead and Similkameen Rivers. Prep. for Coordinating Committee of the Canada-British 

Columbia Water Quality Monitoring Agreement. Environmental Management Associates. 

Page 20 Similkameen River TMDL
Definitions and Acronyms 

CFR Code of Federal Regulations, usually preceded by chapter number and followed 

by a section number (i.e. 40CFR131.36) 

cfs cubic feet per second 

DIP Detailed Implementation Plan 

EPA Unites States Environmental Protection Agency 

g/day grams per day 

NPDES National Pollutant Discharge Elimination System

NTR National Toxics Rule (40CFR131.36) 

RCW Revised Code of Washington 

SIS Summary Implementation Plan 

TMDL Total Maximum Daily Load 

WAC Washington Administrative Code 

WWTP Waste Water Treatment Plant 

μg/L micrograms per liter 

7Q10 The lowest flow averaged over a seven-day period that would be expected to 

occur once every ten years. 

Similkameen River TMDL Page 21 
Page 22 Similkameen River TMDL
Appendix A 

Summary of Public Involvement 

Similkameen River TMDL PageA-1 
PageA-2 Similkameen River TMDL
Summary of Public Involvement 

September 12, 2000 Met with the Okanogan Health District Board to present introductory 

information on the Okanogan DDT/PCB and Similkameen arsenic 

TMDLs. 

November 7, 2000 Presentation on the Okanogan and Similkameen TMDLs made to the 

environmental science class at Wenatchee Community College class at 

the Omak branch campus. 

September 7, 2000 Presentation to the Okanogan Conservation District Supervisor’s 

meeting to introduce the Similkameen arsenic and Okanogan DDT/PCB 

TMDLs 

February 22, 2001 Public meeting at Okanogan PUD to kick -off Okanogan DDT/PCB and 

Similkameen Arsenic TMDLs. 

June 12, 2001 Presentation regarding the Okanogan at the conference “Aquatic 

Ecosystem Health and Fisheries in the Okanogan-Similkameen Basin” 

in Kelona, BC

July 26, 2001 Presentation on the Okanogan DDT/PCB and Similkameen arsenic 

TMDLs to the Okanogan Watershed Implementation committee. 

August 9, 2001 Presentation to the Oroville-Tonasket irrigation District on the 

Okanogan DDT/PCB and Similkameen arsenic TMDLs. 

March 5, 2002 Meeting with the Oroville City Council to discuss arsenic data needed 

from the Oroville wastewater treatment plant. 

April 16, 2002 Meeting to discuss arsenic data results from the sampling the discharge 

of the Oroville wastewater Treatment plant. 

September 10, 2002 Presentation to the Okanogan County Commissioners and invitation to 

participate in the Lower Similkameen watershed tour. 

September 19, 2002 Lower Similkameen Watershed tour including representatives from

Environment Canada, BC Ministry of Water air and Land Protection, 

BC Ministry or Energy & Mines, Okanogan Nations Alliance, Colville 

Confederated Tribes, US Bureau of Land Management, Okanogan 

County Commissioners, Okanogan Public Utility District, Okanogan 

Health District, City of Oroville, and the citizens of Okanogan County. 

October 25, 2002 Meeting with the Okanogan Watershed Implementation Committee to 

discuss the Similkameen River arsenic TMDL and the Okanogan River 

DDT/PCB TMDL 

Similkameen River TMDL PageA-3 
February 24, 2003 Meeting with the Okanogan Watershed Implementation Committee to 

discuss the Similkameen River arsenic TMDL and the Okanogan River 

DDT/PCB TMDL 

July 24, 2003 Meeting with the Okanogan Watershed Implementation Committee to 

discuss the Similkameen River arsenic TMDL and the Okanogan River 

DDT/PCB TMDL 

September 10 to 

October 10, 2003 Public Comment Period for the Similkameen Arsenic TMDL Submittal 

report. Advertised for public comment period and meeting placed in the 

Okanogan Chomical and the Okanogan Valley Gazette Tribune. 

October 1, 2003 Public meeting held in the evening at the Oroville City Hall. Meeting 

provided a forum to discuss the TMDL Submittal Report 

Responses to Comments on the Similkameen Arsenic TMDL 

Submittal Report 

Comments received from David Kliegman, Executive Director of the Okanogan Highlands 

Alliance, Mo McBroom, Staff Attorney for WashPIRG, and Jessica McNamara raised concerns 

that were similar, if not the same as, concerns raised in one other set of comments. Due to these 

similarities, these comments will be addressed together. 

The following comments were received concerning abandoned mines in the Washington’s 

Similkameen Drainage: 

1. The draft plan for monitoring of arsenic TMDLs on the lower Similkameen raises concern 

because the plan lacks any provisions for investigating or addressing possible arsenic 

contamination from the many abandoned mines located in the Similkameen watershed.

According to the Department of Natural Resources' Mas/Mils database, there are 71 abandoned 

mines on the U.S. side of the border in the Similkameen watershed. The majority of these mines 

have never been inventoried or otherwise assessed for their environmental impacts. 

Department of Ecology's TMDL evaluation completed in 2002 acknowledges the existence of 

only 11 of the Similkameen watershed's 71 mines. The 60 mines not mentioned in the report 

contain tens of thousands of miles of stopes, drifts, shafts and adits, as well as unknown acres of 

tailings and waste rock piles, any of which could be sources of arsenic to the Similkameen River 

and Palmer Creek. 

With respect to the 11 mines that were considered in the TMDL evaluation, it appears that 

Ecology looked only for obvious evidence of off-site drainage, and did not test for arsenic levels, 

nor conduct other tests such as trace element doping to verify whether arsenic or other metals 

from these mines may be migrating within the watershed. Nor has Ecology taken measures to 

determine whether any of the 71 mines are contributing particulate arsenic to the Similkameen 

PageA-4 Similkameen River TMDL
River or Palmer Creek through erosion and sediment generation during spring freshets. Ecology's 

conclusion in the TMDL draft report that arsenic loading in the watershed occurs from sources 

"mostly in British Columbia" is weakened by the complete lack of information about these 

Washington mine sites. 

Without adequate data on these potential sources of contamination to the watershed, we are 

concerned that Ecology cannot properly implement a plan to monitor non-point sources and 

ensure adequate implementation of the TMDL. 

Federal law requires Washington State to identify sources of pollution in waters that fail to meet 

state water quality standards, and to develop water cleanup plans to address those pollutants. 

Despite this mandate, the TMDL process for the Similkameen River currently lacks substantive 

information that could be used to confirm whether or not the 71 abandoned mines in the 

Similkameen watershed are sources of arsenic to the river. 

For this reason, we request that you revise the TMDL to include an assessment of the potential 

for arsenic contribution into the Similkameen River from each of these 71 mine sites. We 

understand that the Department of Natural Resource (DNR) has a program for the inventory of 

the state's abandoned mines and we respectfully suggest that Ecology might work with DNR to 

procure the necessary information on the mines in the Similkameen watershed. 

Response: Ecology’s approach to the investigation of Arsenic in the Similkameen River 

in this TMDL has been to first examine the arsenic concentrations in the Similkameen 

River reach by reach, and then identify potential arsenic sources associated with elevated 

reach concentrations. By starting the investigation at the known points of water quality 

impairment and working into more detailed divisions of the river to determine where 

significant loading to the river occurs, Ecology is identifying those sources that have the 

most significant impact on water quality. Ecology’s TMDL investigation did show a 

significant contribution to the Similkameen’s arsenic load from Palmer creek and the 

Reach of River from river mile 19.2 to 23.8. This reach is dominated by the accumulation 

of sediments deposited by high flows in the Similkameen River. These sediment deposits, 

whose source is higher in the Similkameen Watershed, appear to be the source of arsenic 

producing elevations of dissolved arsenic in the river most of the year. 

The Similkameen Arsenic TMDL examined potential surface water connections and 

influence of the larger mines in Washington’s Similkameen River drainage. The TMDL 

investigation did not find direct links between the hard rock metals mines in Washington 

and the arsenic loading in the Similkameen River. The November 1990 Washington State 

Department of Natural Resources report “Metal Mines of Washington- Preliminary 

Report” shows that each of the largest mines in the region have less than a mile of 

underground workings. Sixty mines could not possibly account for “tens of thousands of 

miles of stopes, drifts, shafts and adits, as well as unknown acres of tailings and waste 

rock piles”. 

Ecology is participating with Washington Department of Natural Resources in the 

assessment of abandoned mines in Washington. Much of the assessment project is a joint 

Similkameen River TMDL PageA-5 
effort between Ecology Staff and DNR staff. Ecology has published the first part of the 

assessment project’s findings as the report titled: Screening Level Investigation of 

Water and Sediment Quality of Creeks in Ten Eastern Washington Mining 

Districts, with Emphasis on Metals. This publication is number 00-03-004 and is 

available from Ecology’s publication office or it can be viewed on line at 

http://www.ecy.wa.gov/pubs/0003004.pdf . 

2. The proposed schedule for periodic monitoring only every five years, and monitoring only 

during ten-year high water events, is inadequate to provide the information necessary for 

compliance with the Clean Water Act. Even though the DOE may not anticipate new sources of 

arsenic, there are several reasons why an annual, or at least semi-annual, monitoring should 

continue, at least for a few more years. 

Response: Ecology doesn’t expect changes to become evident in the space of a single 

year, and we believe that our current data base gives us adequate insight into variability 

on shorter time scales. 

3. The data from monthly monitoring from May 2000 to June 2001 occurred over a period of 

low precipitation and spring run-off. This does not reflect the years when above normal flows 

and flood events occurred, so a true picture does not emerge. In addition, the report asserts, "the 

downward trend in arsenic concentrations may be due in part or in whole to changes in analytical 

techniques over the time monitoring has occurred". It seems then that the results obtained, i.e., 

improved lower levels of arsenic, are open to question. Waiting another five years to establish 

new measurements to corroborate whether this improvement has really occurred is questionable. 

Response: The arsenic contamination in the Similkameen River is from natural sources 

combined with the legacy of a hundred years of mining history in the region. The long 

term monitoring program is appropriate for this situation and will account for variations 

in weather over time. 

4. There is no consideration given to the fact that mining IS currently occurring in portions of 

the Similkameen both above and below Enloe Dam. Though this is considered "recreational 

mining" (i.e., gold dredging), there has been very little research done as to the extent and effects. 

Currently the DNR has permit applications for 25 dredges in the river, some of these possibly 

commercial, which they neither may nor may not have yet approved. In addition, the Dredge 

Earth First rally is now planned as an annual event which could bring several thousand people 

into the area every August, many of whom will be dredging both during and possibly after the 

rally. Without a continuing monitoring program there will be no way of knowing what effects 

this amount of dredging will have on TMDLs and what precautions may need to occur. 

Response: To address concerns relating to the affect of recreational dredge mining on 

the arsenic values of the Similkameen River, a field investigation of the effects of dredge 

mining on arsenic loading in the Similkameen River has now been added to the 

implementation strategy. The planned investigation will be undertaken to determine the 

applicability of the dredge simulation study conducted by Ecology in 1999 to the arsenic 

PageA-6 Similkameen River TMDL
TMDL. Ecology will use an in-river study to better determine the water quality impacts 

of recreational dredging conducted according to the rules and regulations for mineral 

prospecting and placer mining in Washington State as administered by the Washington

State Department of Fish and Game. This study should provide information that can be 

applied to the individuals or organized groups operating within the Similkameen River. 

Those concerned about the regulation of recreational dredging should be aware of the 

upcoming revision of the WDFW’s rules and regulations for mineral prospecting and 

placer mining in Washington Sate. Opportunities for public involvement could begin as 

early as the spring of 2004. 

In response to comments received by Ecology, an inquiry was made to Washington 

Department of Natural Resources (DNR) on the status of pending dredge applications in 

the Similkameen River. The response from DNR was that the six outstanding 

applications for dredge mining have recently been denied and there are no outstanding

applications at this time. (Personal communication with Mike Rechner, DNR aquatic 

lands, December 2003). 

5. The high arsenic levels at Palmer Lake/Creek may be strictly a result of the washing out of 

the sediments from Palmer Creek into the Similkameen during the high spring flows, but more 

consideration and study need to be done on the role of Sinlahekin Creek in adding several 

hundred thousand tons of sediment to Palmer Lake annually. This sediment, both that which 

remains in the lake and that which flows into the Similkameen, may also be contributing to 

arsenic totals. As yet, there are no conclusions as to the amount of sediment, where and why it is 

occurring, or the improved management practices necessary to moderate it. Several large 

landslides, caused by poor logging and roading practices, have occurred in the past 20 years. If 

Sinlahekin Creek is a factor in increased arsenic levels in Palmer Lake and the Similkameen, 

then there is a need to analyze and correct this, since it is within the U.S. boundaries. 

Response: Sediment transport by Sinlahekin Creek has not been specifically addressed 

in the information included in the Similkameen arsenic assessment report. The Okanogan 

Conservation District has monitored Sinlahekin Creek as part of the Okanogan 

Watershed Water Quality Management Plan and measured the total suspended solids in 

the creek between 1 and 10 milligrams per liter and flows from 12 to 83 cubic feet per 

second. The highest values of suspended solids did occur during the highest measured 

flow, but even if this high flow were maintained year around the sediment transport into 

Palmer Lake would not approach hundreds of thousands of tons. Please consider 

providing the information you have regarding sediment transport by Sinlahekin Creek so 

that Ecology can evaluate it during development of the detailed implementation plan. 

Similkameen River TMDL PageA-7 
Comments Received from the Colville Confederated Tribes: 

CCT 1. As acknowledged by the author, historical data used to support the conclusion that 

Similkameen River water quality is improving is incomparable, contradicted seasonally, and may 

in fact demonstrate a decline in water quality over time. Yet the specious trend is used to justify 

DOE’s strategy to rely solely on water monitoring as a method to achieve compliance with water 

quality standards. 

Response: The monitoring strategy presented in the Summary Implementation Strategy 

is intended to examine the long term trend in the arsenic loading of the Similkameen 

River. Ecology acknowledged that the data set developed for this TMDL is limited by the 

climatic conditions occurring during the study year. Long term monitoring is needed to 

truly determine the condition of the river with differing climatic conditions. Additionally, 

the long term monitoring plans will incorporate the review of any additional data 

available from non-Ecology sources prior to the monitoring cycle. This will include any 

additional data available from Canadian sources as indicated in the actions recommended 

at the conclusion of the TMDL technical report. Should the long - term monitoring set out 

in the submittal report show a rising trend in the arsenic concentrations, then additional 

investigations and actions included in the adaptive management section of the report will 

be undertaken. 

CCT 2. The long term monitoring plan is pared down significantly from recommendations 

contained in the TMDL Evaluation for Arsenic in the Similkameen River. No new data was 

reported in the SIS that warrants a less rigorous sampling plan. Logic for the diminished 

monitoring plan appears to be a concession to the legacy of mining and is inconsistent with goals 

and objectives of the Clean Water Act. 

Response: Most of the recommended actions in the technical report will be incorporated 

into the long term monitoring plan included in the SIS. Periodic review of Canadian data 

will be incorporated into the five-year sampling cycle included in the SIS. Coring of

sediments was considered by the Okanogan Water Quality Management Plan’s 

Implementation Committee, but was not included in the SIS as is was not expected to 

change the options or actions available to address arsenic in the Similkameen River. 

The analysis of fish tissue, as suggested in the technical report, was not seen as an action 

that would contribute to the reduction of arsenic in the Similkameen river system, but 

should be conducted outside the construct of the TMDL process. The Washington State 

Department of Ecology partners with the Washington State Department of Health to 

address health concerns relating to fish consumption. A sampling of fish tissue for arsenic 

was included in the Ecology study titled “Investigation of Background Inorganic and 

Organic Arsenic in Four Washington Lakes.” Conner’s Lake in the SimilkameenSinlahekin watershed was included in this study. The results of this study support the 

need for a fish tissue study in Palmer Lake. Ecology will consider conducting a fish tissue 

study for Palmer Lake and the priority of the project relative to other water quality 

projects proposals. 

PageA-8 Similkameen River TMDL
CCT 3. True, active point sources upon which to focus remedial measures are problematical on 

the Similkameen River in the US. Instead, most of the ongoing releases of arsenic appear to 

derive through recycling of contaminated sediments by re-suspension of fine- grained bank 

materials. The sediment source is near surface and as wide as the floodplain. The SIS must 

summarize in the SIS for more careful development in the DIP those practically available 

remedial measures capable of increasing bank stability and decreasing flood-driven resuspension of sediments. These include Best Management Practices for livestock grazing. The 

potential for sediment stabilization through bank revegetation programs should be included in the 

SIS. Institutional controls should also be explored. 

Response: Ongoing release of arsenic takes two forms in the Similkameen River. 

Release through re-suspension of sediment occurs during the high water/high flow events 

and release of dissolved arsenic occurs as a result of the long term contact of arsenicenriched material with the waters in the Similkameen river system. 

Re-suspension of the sediments from the Similkameen River is a function of river 

dynamics in this area. The Similkameen River in the reach between the international 

border and the entrance to the Similkameen River Canyon, at river mile 19.5, is 

characterized by multiple channels and a wide and active floodplain. The sediments it 

transports are from both the current stream bed and the adjacent banks, where the banks 

are unstable. Stream bank erosion in this type of system is typified by infrequent 

avulsions of the stream channels as increasing sediment deposits force channel changes. 

When channel avulsion occurs, the new channel transports sediment from an area that 

may have higher or lower arsenic concentration than the previous channel. 

Dissolved arsenic is the result of the contact between river water and river sediments that 

are elevated in arsenic. These releases of dissolved arsenic, primarily in the vicinity of the 

Palmer Creek confluence, create the rise in arsenic loading to the river that is seen 

between the international boundary and the city of Oroville. The dissolved arsenic 

loading is the primary concern during most of the year, while arsenic-enriched sediment 

transport is dominant during the relatively short high water portion of the annual cycle. 

Reducing or eliminating the sources of arsenic-rich sediments that are deposited in this 

river reach would address both loading concerns for suspended sediments and dissolved 

arsenic. However, significant localized sources of arsenic-rich materials contributing to 

the sediments in the Similkameen River were not identified in the segment of river 

addressed by this TMDL. Further monitoring would be required in order to determine 

whether re-suspension of bank sediments in Palmer Lake and Palmer Creek is increasing 

in-stream arsenic concentrations. 

CCT 4. ...recreational dredging should be discouraged because it aggressively re-entrains 

arsenic contaminated bed sediment. The potential adverse effect of recreational dredging in 

arsenic contaminated sediments is further reason to discourage the practice on the Similkameen. 

Response: Addressed with the dredge mining comments above by WASHPIRG, 

Okanogan Highlands Alliance and J. McNamara. 

Similkameen River TMDL PageA-9 
CCT 5. Available measures to help minimize flooding in the United States should be 

summarized in the SIS. The Similkameen River valley is highly channelized in the Canadian 

(upstream) reach of the river. DOE should coordinate with upstream B.C. land management 

agencies to reduce flooding in the Palmer Lake/Similkameen River basin by removing upstream

levees and riprap where feasible and avoiding further construction of channeling structures. 

Response: The scope of this TMDL is limited to that portion of the Similkameen River 

that flows through Washington State. However, the Similkameen River that flows 

through Washington is greatly influenced by the conditions in Canada. The Okanogan 

Conservation District and the National Resources Conservation Service have considered 

and rejected stream bank stabilization in the Washington Reach of the Similkameen 

because it would need to be on the same scale as the Canadian river channel controls to 

have a chance of resisting the river forces associated with the release of water from the 

diked river channel in Canada. It also needs to be acknowledged that this scale of stream 

stabilization would eliminate the function of the floodplain that still exists in Washington 

and push erosion and sediment related problems to the next river segment downstream. If 

however, it is determined that re-suspension of bank sediment in Palmer Lake and Palmer 

Creek is increasing in-stream arsenic concentrations, it would be appropriate to 

coordinate with upstream B.C. land management agencies to discuss upstream measures 

that would decrease flooding in the Palmer Lake / Similkameen River basin. 

CCT 6. Based on the above, and on the fact that if the DOE is hoping to work with Canada on 

lowering arsenic levels on their section of the river, it seems necessary to continue a more 

thorough and reliable arsenic monitoring program than the one currently recommended in the 

draft report. 

Response: We believe the proposed monitoring program is appropriate for these 

purposes. The use of adaptive management discussed in the report provides the ability to 

respond through the TMDL to additional data as it becomes available. 

PageA-10 Similkameen River TMDL
Appendix B 

Technical Report 

A Total Maximum Daily Load Evaluation for Arsenic in the Similkameen River

November 2002 

Ecology Publication Number 02-03-044 

This publication may be viewed at the following website: 

http://www.ecy.wa.gov/biblio/0203044.html

Paper copy may be obtained upon request.

Similkameen River TMDL PageB-1